The Epic Games directory discussion should identify which Epic service an integration actually needs. Epic Online Services account authentication and game-service identity are related but not interchangeable.
Epic's Connect login guide describes exchanging an authenticated account context for a Product User ID. Do not treat that product-scoped identifier as a universal account identifier across unrelated products.
Start with the documented interface for your use case. A request observed in a storefront's browser traffic is not, by itself, a supported public API contract for a new application.
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